Experimental Progress on Zonal Flow Physics in Toroidal Plasmas

Present status of experiments on zonal flows is overviewed. Innovative use of traditional and modern diagnostics has revealed unambiguously the existence of zonal flows, their spatio-temporal characteristics, their relationship with turbulence, and their effects on confinement. Particularly, a number of observations have been accumulated on the oscillatory branch of zonal flows, dubbed geodesic acoustic modes, suggesting necessity of theories to give their proper description. In addition to these basic properties of zonal flows, several new methods have elucidated the zonal flow generation processes from turbulence. Further investigation of relationship between zonal flows and confinement is strongly encouraged as cross-device activity including low temperature toroidal and linear devices. Experimental Progress on Zonal Flow Physics in Toroidal Plasmas 3